NCERT Solutions class 8 Science 14. Chemical Effects of Electric Current Text Book Exercise

exercise

1. Fill in the blanks

(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.

(b) The passage of an electric current through a solution causes ______________ effects.

(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the terminal of the battery.

(d) The process of depositing a layer of any desired metal on another material by means of electricity is called .

Answer:

(a) acids, bases, salts, (b) chemical, (c) negative, (d) electromagnet.

2. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Answer:

Yes, it is because the solution conducts electricity.

3. A tester is used to check the conduction of electricity through two liquids, labeled A and B.

It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. You would conclude that

(i) liquid A is a better conductor than liquid B.

(ii) liquid B is a better conductor than liquid A.

(iii) both liquids are equally conducting.

(iv) conducting properties of liquid cannot be compared in this manner.

Answer:

(i) Liquids A is better conductor than liquid B.

4. Does pure water conduct electricity? If not, what can we do to make it conducting?

Answer:

Pure water does not be conduct electricity. It can be made conducting if acid, base or salt is dissolved in it.

5. In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.

Answer:

The water used to extinguish fire, have lot of minerals and dissolved salts, which make it conducting. Before throwing it water into the burning houses, the burning houses, the mains of electricity of the area is turned off because then the water may conduct huge current and firemen get electrocuted.

6. A child staying in a coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?

Answer:

The impure water is conductor of electricity. Sea water contains more impurity than drinking water. Therefore, sea water conducts more electricity than the drinking water. That is why, compass needle deflects more in case of sea water.

7. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Answer:

When it rains heavily, the rain water dissolves many impurities from the atmosphere which makes is impure and hence conductive. The air too becomes humid with this water and behaves as a conductor to electricity. That is why, it is not wise for eletrician to do electrical repair work when it rains heavily, becuse he may get dreadful shock or even gets electrocuted.

8. Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reasons?

Answer:

Rain water is, of cource, as good as distilled water but, when it passe s through atmosphere, it dissolves a lot of dust, dirt and impurities and becomes conductive. So, when Paheli used a tester, its compass showed deflection. 

9. Prepare a list of objects around you that are electroplated.

Answer:

(i) Tap of water connection,

(ii) Parts of bicycle,

(iii) Body of cars, motor cycle ahd tractors,

(iv) Handle of the doors, etc.